The present invention relates to a device for adjusting the position and the orientation around an axis of a sample holder for an electron microscope. It finds a particularly important application in very high voltage electron microscopes, of 1 MeV and higher.
It is known that electron microscopes are particularly used for studies which require the possibility of adjusting not only the position of the sample in a plane (to select the point observed) and in height, but also its inclination. Devices permitting these functions to be carried out are called "goniometric plate" devices.
The variations in inclination of the sample holder must not to be manifested either by movement of the sample in its plane, which would lead to a change in the zone observed, nor by a vertical movement which would necessitate refocusing, which operation would result in its turn in a change in magnification and, if the microscope is a magnetic optical microscope, a rotation of the image.
To avoid any interaction of the inclination movement with the translation movements, the axis of inclination must remain concurrent with the electron beam which determines the zone observed. A device corresponding to this condition is called a "eucentric goniometric plate" device. To constitute this, it is necessary in particular for the controls of translation movement to be borne by a unit of the device which can be inclined as a block.
The majority of existing eucentric goniometric plate devices for an electron microscope with lateral entry are of the type comprising a support tube passing through the wall of the column of the microscope, whose inner end is supported on an internal structure of the microscope by a hemispherical surface, which is supported in the wall of the column by means permitting it to rotate around the axis of orientation, and which is connected to the sample holder which passes through it, by control means enabling adjustment of the position of the sample holder in the support tube along the three axes of a reference trihedral.
The sensitivity and the resolution which can be achieved by currently known devices of this type are relatively satisfactory in conventional electron microscopes of 100 and 200 KV. This is not the case for high voltage microscopes due to the fact in particular of the increase in diameter of the column, which reaches 500 mm from a voltage of 1 MV, instead of about 200 mm at 200 KV. In fact, these devices have overhangs such that the deformations in flexion become notable and weights such that the solid friction to be overcome is manifested by jerky movements.
It is an object of the present invention to provide a device of the above-defined type avoiding appreciable deformations and frictions of guidance and articulation which cause jerky movements detrimental to sensitivity and permitting the sample to be made fast with the column, any relative movement between the sample and the column limiting the overall resolution of the microscope.